Process for the production of jet-range hydrocarbons

ABSTRACT

A method for producing jet-range hydrocarbons includes passing a renewable olefin feedstock comprising C 3  to C 8  olefins to an oligomerization reactor containing a zeolite catalyst to produce an oligomerized effluent, separating the oligomerized effluent into at least a light stream, and a heavy olefin stream. At least a first portion of the heavy olefin stream is recycled to the oligomerization reactor to dilute the renewable olefin feedstock. portion of heavy olefin stream may be hydrogenated and separated to provide a jet range hydrocarbon product.

FIELD OF THE INVENTION

The present disclosure generally relates to methods for producingrenewable fuels and chemicals from biorenewable sources and therenewable fuels and chemicals produced thereby, and more particularlyrelates to methods for producing jet-range hydrocarbons from alkanols,including for example isobutanol, and the jet-range hydrocarbonsproduced thereby.

BACKGROUND OF THE INVENTION

As the worldwide demand for fuel increases, interest in sources otherthan crude oil from which to produce transportation fuels, includingaviation fuels, is ever increasing. For example, due to the growingenvironmental concerns over fossil fuel extraction and economic concernsover exhausting fossil fuel deposits, there is a demand for using analternate or “green” feed source for producing hydrocarbons for use astransportation fuels and for use in other industries. Such sources ofinterest include, for example, biorenewable sources, such as vegetableand seed oils, animal fats, and algae byproducts, among others as arewell-known to those skilled in the art. conventional catalytichydro-processing technique is known for converting a biorenewablefeedstock into green diesel fuel that may be used as a substitute forthe diesel fuel produced from crude oil. As used herein, the terms“green diesel fuel” and “green jet fuel” refer to fuel produced frombiorenewable sources, in contrast to those produced from crude oil. Theprocess also supports the possible co-production of propane and otherlight hydrocarbons, as well as naphtha or green jet fuel.

Biomass fermentation products typically include lower isoalkanols suchas, for example, C₃ to C₈ isoalkanols obtained by contacting biomasswith biocatalysts that facilitate conversion (by fermentation) of thebiomass to isoalkanols of interest. The biomass feedstock for suchfermentation processes can be any suitable fermentable feedstock knownin the art, such as fermentable sugars derived from agricultural cropsincluding sugarcane, corn, etc. Suitable fermentable biomass feedstockcan also be prepared by the hydrolysis of biomass, for examplelignocellulosic biomass (e.g. wood, corn stover, switchgrass, herbiageplants, ocean biomass, etc.), to form fermentable sugars.

Jet-range fuels are an important product for the aerospace industry andthe military. The specific characteristics of various grades and typesof jet-range fuels vary slightly according to the particular applicationand environment in which they are used. Generally, jet-range fuelscomprise a mixture of primarily C₈ to C₁₆ hydrocarbons and typicallyhave a freezing point of about −40 or −47° C. (−40 or −52.6° F.). Inorder to produce jet-range fuels from isoalkanols derived from fermentedbiomass, in one example known in the art, isobutanol is first dehydratedto form butenes. The butenes are then oligomerized, in the presence ofan oligomerization catalyst, in one or more reactors to form heavierolefins, such as C₅ to C₂₀, or even higher, olefinic oligomers. Finally,the resulting olefinic oligomers are hydrogenated in a saturationreactor to form the corresponding C₅ to C₂₀, or even higher, paraffinsin a mixture which can then be subjected to separation to obtain C₉ toC₂₀₊ paraffins suitable for use as biorenewable jet fuel.

Since the oligomerization reaction is highly exothermic, the butene fedto the oligomerization reactors may be cooled before entering theoligomerization reactors. Another measure taken to control thetemperature increase in the oligomerization reactors is to limit theproportion of olefins contained in the feedstream provided to eachreactor to no more than about 15 percent by weight (wt %). This isaccomplished, at least in part, by adding non-reactive diluent materialto the reactors which also provides a heat sink to control thetemperature rise in the reactors.

Typically, this dilution may be done by recycling saturated distillateproduct from a stripped effluent of a hydrogenation section back to theoligomerization and hydrogenation reactors. Hydrogen transfer from thesaturated diluent to the light olefinic feed to the oligomerizationreactor can cause yield loss by saturating the light olefin feeds intoparaffins. Paraffins, however, will not participate in theoligomerization reactions and will be recovered as saturated liquefiedpetroleum gas, instead of olefinic distillate range material. Since thedesired product is a distillate range material, conversion of theolefins into saturated liquefied petroleum gas amounts to a loss ofpotential distillate yield, and thus is considered undesirable.Therefore, it would be desirable to have one or more processes in whichthe dilution of the feedstock to the oligomerization reactor is lesslikely to result in yield loss.

SUMMARY OF THE INVENTION

One or more processes have been invented in which a portion of an olefineffluent from an oligomerization reaction is used to dilute thefeedstock to the oligomerization reaction.

In a first aspect of the invention, the present invention may be broadlycharacterized as a providing a process for producing jet rangehydrocarbons by oligomerizing a renewable olefin feedstock comprising C₃to C₈ olefins in an oligomerization reactor containing a catalyst andbeing operated under conditions to produce an oligomerized effluent;separating the oligomerized effluent to produce a light hydrocarbonstream, a naphtha hydrocarbon stream, and a heavy stream comprising C₈+olefins; splitting the heavy stream into a first portion and a secondportion; and, diluting the renewable C₄ olefin feedstock with the firstportion of the heavy stream.

In one or more embodiments of the present invention, the process furthercomprises controlling a flow rate of the first portion of the heavystream. It is contemplated that the flow rate of the first portion ofthe heavy stream is controlled to obtain a desired ΔT in theoligomerization reactor of at least 25° C. and no more than 60° C.

In various embodiments of the present invention, the process furthercomprises hydrogenating the second portion of the heavy stream in ahydrogenation zone having a hydrogenation reactor to provide ahydrogenated effluent. It is contemplated that the process includesseparating the hydrogenated effluent into a vent gas stream and asaturated hydrocarbons stream. It is further contemplated that theprocess includes separating the saturated hydrocarbons stream into asaturated jet range stream and a saturated diesel range hydrocarbonsstream. It is still further contemplated that the process includesrecycling at least a portion of the saturated hydrocarbons stream to thehydrogenation zone.

In a second aspect of the present invention, the present invention maybe generally characterized as providing a process for producing jetrange hydrocarbons by: passing a renewable olefin feedstock comprisingC₃ to C₈ olefins to an oligomerization reaction zone comprising anoligomerization reactor containing a catalyst and being operated underconditions to produce an oligomerized effluent; passing the oligomerizedeffluent to a first separation zone to provide at least one streamcomprising C⁷⁻ hydrocarbons and a C₈+ olefin stream; splitting the C₈+olefin stream into a first portion and a second portion; and, recyclingthe first portion of the C₈+ olefin stream to the oligomerizationreaction zone.

In one or more embodiments of the present invention, the process furthercomprises combining the first portion of the C₈+ olefin stream with therenewable C₄ olefin feedstock to provide a combined stream and passingthe combined stream into the oligomerization reactor.

In at least one embodiment of the present invention, the firstseparation zone produces a light hydrocarbon stream and a naphthahydrocarbon stream.

In some of the embodiments of the present invention, the process furthercomprises passing the second portion of the C₈+ olefin stream to ahydrogenation zone having a hydrogenation reactor containing a catalystand being operated to provide a hydrogenated effluent. It iscontemplated that the process includes passing the hydrogenated effluentto second separation zone to provide at least a vent gas stream and asaturated jet range stream. It is also contemplated that the processincludes recycling a portion of the hydrogenated effluent to thehydrogenation zone as a recycle stream. It is further contemplated thatthe process includes combining the recycle stream and the second portionof the C₈+ olefin stream into a combined stream and, passing thecombined stream to the hydrogenation reactor.

In one or more of the embodiments of the present invention, the processfurther comprises passing the hydrogenated effluent to a secondseparation zone having at least two columns. It is contemplated that afirst column in the second separation zone separates the hydrogenatedeffluent into a vent gas stream and a saturated hydrocarbon stream. Itis also contemplated that a second column in the second separation zoneseparates the saturated hydrocarbon stream into a saturated jet rangestream and a saturated diesel stream. It is further contemplated thatthe process includes passing at least a portion of the saturatedhydrocarbon stream to the hydrogenation reaction zone as a recyclestream.

In at least one of the embodiments of the present invention, the processfurther comprises controlling a temperature rise in the oligomerizationreactor by adjusting a flow rate of the first portion of the C₈+ olefinstream.

In some of the embodiments of the present invention, the process furthercomprises increasing a flow rate of the first portion of the C₈+ olefinstream to decrease a temperature rise in the oligomerization reactor.

Additional aspects, embodiments, and details of the invention, which maybe combined in any manner, are set forth in the following detaileddescription of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

One or more exemplary embodiments of the present invention will bedescribed below in conjunction with the following drawing FIGURE, inwhich:

the FIGURE shows a process flow diagram of one or more processesaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “stream” can include various hydrocarbonmolecules and other substances. Moreover, the term “stream comprisingC_(x) hydrocarbons” or “stream comprising C_(x) olefins” can include astream comprising hydrocarbon or olefin molecules, respectively, with“x” number of carbon atoms, suitably a stream with a majority ofhydrocarbons or olefins, respectively, with “x” number of carbon atomsand preferably a stream with at least 75 wt % hydrocarbons or olefinmolecules, respectively, with “x” number of carbon atoms. Moreover, theterm “stream comprising C_(x)+ hydrocarbons” or “stream comprisingC_(x)+ olefins” can include a stream comprising a majority ofhydrocarbon or olefin molecules, respectively, with more than or equalto “x” carbon atoms and suitably less than 10 wt % and preferably lessthan 1 wt % hydrocarbon or olefin molecules, respectively, with x−1carbon atoms. Lastly, the term “C_(x)− stream” can include a streamcomprising a majority of hydrocarbon or olefin molecules, respectively,with less than or equal to “x” carbon atoms and suitably less than 10 wt% and preferably less than 1 wt % hydrocarbon or olefin molecules,respectively, with x+1 carbon atoms.

As used herein, the term “zone” can refer to an area including one ormore equipment items and/or one or more sub-zones. Equipment items caninclude one or more reactors or reactor vessels, heaters, exchangers,pipes, pumps, compressors, controllers and columns. Additionally, anequipment item, such as a reactor, dryer, or vessel, can further includeone or more zones or sub-zones.

As used herein, the term “substantially” can mean an amount of at leastgenerally about 70%, preferably about 80%, and optimally about 90%, byweight, of a compound or class of compounds in a stream.

As used herein, the term “gasoline” can include hydrocarbons having aboiling point temperature in the range of about 25 to about 200° C. (68to 392° F.) at atmospheric pressure.

As used herein the term “naphtha” can mean C₅ hydrocarbons up tohydrocarbons having a boiling point of 150° C. (302° F.) (i.e.,hydrocarbons having a boiling point in the range of 30 to 150° C. (86 to302° F.)).

As used herein the term “diesel” can include hydrocarbons having aboiling point temperature in the range of about 250 to about 400° C.(482 to 752° F.) at atmospheric pressure.

As used herein the term “jet-range hydrocarbons,” “jet-range paraffins,”“jet-range fuels,” or “jet fuels” can include hydrocarbons having aboiling point temperature in the range of about 130 to about 300° C.(266 to 572° F.), preferably 150 to 260° C. (302 to 500° F.), atatmospheric pressure. Additionally, as used herein, the terms “jet-rangehydrocarbons,” “jet-range paraffins,” “jet-range fuels,” or “jet fuels”refer to a mixture of primarily C₈ to C₁₆ hydrocarbons with a freezingpoint of about −40° C. (−40° F.) or about −47° C. (−52.6° F.).

As used herein, the term “distillate” comprises a mixture of diesel andjet-range hydrocarbons and can include hydrocarbons having a boilingpoint temperature in the range of about 150 to about 400° C. (302 to752° F.) at atmospheric pressure.

As used herein, the phrase “a mixture of primarily . . . ” or“comprising primarily . . . ” a specified range of carbon-numberedhydrocarbons means that the group or category of hydrocarbons beingdescribed may also contain very small amounts of hydrocarbons outsidethe stated carbon number range, without altering the generalcharacteristics (e.g., boiling point) of the group or category beingdescribed. For example, the description that jet fuels are a mixture ofprimarily C₈ to C₁₆ hydrocarbons means that jet fuels contain at least80 wt % of hydrocarbon molecules each having from about 8 to about 16carbon atoms with, possibly, very small amounts of hydrocarbon moleculeseach having less than about 8 carbon atoms, as well as very smallamounts of hydrocarbon molecules each having more than 16 carbon atoms,such that the freezing point remains about −40° C. to about −47° C. (−40to 52.6° F.). There are multiple standards, established by variousindustries and governments, that are useful for ensuring that particulartypes of jet fuels have uniform characteristics that fall withinexpected ranges. For example, one type of jet fuel, known as AviationTurbine Fuel, Jet A, or Jet A-1 fuel, is composition of hydrocarbonsthat boil in a range such that the volatility characteristics of thehydrocarbon (or paraffinic form of the hydrocarbon after hydrogenation)substantially conform to the volatility standards of flash point(typically minimum of 38° C. (100° F.), distillation range (T10 boilingpoint maximum of 205° C. (401° F.) and final boiling point (maximum of300° C. (572° F.), with all distillation valves measured by D86 or D2887values converted to D86) set forth in ASTM D7566-11a, “StandardSpecification for Aviation Turbine Fuel Containing SynthesizedHydrocarbons,” promulgated by ASTM International, Inc. of WestConshohoken, Pa. Other standards that provide parameters useful forcharacterizing and defining the jet fuels prepared using the methods andapparatus contemplated and described herein include Jet Propellant(JP)-5 and JP-8, which are set forth in the United States militaryspecifications found at MIL-DTL-83133, as well as in British DefenceStandard 91-87.

The term “column” means a distillation column or columns for separatingone or more components of different volatilities. Unless otherwiseindicated, each column includes a condenser on an overhead of the columnto condense and reflux a portion of an overhead stream back to the topof the column and a reboiler at a bottom of the column to vaporize andsend a portion of a bottom stream back to the bottom of the column.Feeds to the columns may be preheated. The top pressure is the pressureof the overhead vapor at the outlet of the column. The bottomtemperature is the liquid bottom outlet temperature. Overhead lines andbottom lines refer to the net lines from the column downstream of thereflux or reboil to the column.

As used herein, the term “boiling point temperature” means atmosphericequivalent boiling point (AEBP) as calculated from the observed boilingtemperature and the distillation pressure, as calculated using theequations furnished in ASTM D1160 appendix A7 entitled “Practice forConverting Observed Vapor Temperatures to Atmospheric EquivalentTemperatures.”

As used herein, “taking a stream from” means that some or all of theoriginal stream is taken.

Disclosed herein are methods and apparatus for producing jet-rangehydrocarbons from one or more biorenewable C₃ to C₈ olefins viaoligomerization. As mentioned above, the oligomerization reaction ishighly exothermic. In order to control the temperature rise from theinlet to the outlet in the reactor (i.e., the “ΔT”), various processesutilize a diluent. However, it has been discovered that by using aportion of the heavy olefins produced in the oligomerization reactor,the temperature rise can be controlled without using paraffinhydrocarbons which can result in hydrogen transfer to the olefins in theoligomerization reactor. The heavy olefins have been found to resistfurther oligomerization, resulting in a diluent that can minimize yieldloss. While these methods find greatest utility in converting feedstocksfrom alkanols, thereby allowing for production of jet fuels fromrenewable sources, this is not intended to limit the application of themethods of the present invention.

With these general principles in mind, one or more embodiments of thepresent invention will be described with the understanding that thefollowing description is not intended to be limiting.

As shown in the FIGURE, one or more processes of the present inventioninclude a renewable olefin feedstock 10 being passed to anoligomerization zone 12. As used herein, the term “renewable” denotesthat the carbon content of the olefin feedstock 10 is from a “newcarbon” source as measured by ASTM test method D6866-05, “Determiningthe Bio-based Content of Natural Range Materials Using Radiocarbon andIsotope Ratio Mass Spectrometry Analysis”, incorporated herein byreference in its entirety. This test method measures the ¹⁴C/¹²C isotoperatio in a sample and compares it to the ¹⁴C/¹²C isotope ratio in astandard 100% bio-based material to give percent bio-based content ofthe sample. Additionally, “bio-based materials” are organic materials inwhich the carbon comes from recently (on the order of centuries) fixatedcarbon dioxide present in the atmosphere using sunlight energy(photosynthesis). On land, this carbon dioxide is captured or fixated byplant life (e.g., agricultural crops or forestry materials). In theoceans, the carbon dioxide is captured or fixated by photosynthesizingbacteria or phytoplankton. For example, a bio-based material has a¹⁴C/¹²C isotope ratio greater than zero. Contrarily, a fossil-basedmaterial has a ¹⁴C/¹²C isotope ratio of zero. The term “renewable” withregard to compounds such as alcohols or hydrocarbons (olefins,di-olefins, polymers, etc.) also refers to compounds prepared frombiomass using thermochemical methods (e.g., Fischer-Tropsch catalysts),biocatalysts (e.g., fermentation), or other processes, for example asdescribed herein.

A small amount of the carbon atoms in the carbon dioxide in theatmosphere is the radioactive isotope ¹⁴C. This ¹⁴C carbon dioxide iscreated when atmospheric nitrogen is struck by a cosmic ray generatedneutron, causing the nitrogen to lose a proton and form carbon of atomicmass 14 (¹⁴C), which is then immediately oxidized, to carbon dioxide.small but measurable fraction of atmospheric carbon is present in theform of ¹⁴C.

Atmospheric carbon dioxide is processed by green plants to make organicmolecules during the process known as photosynthesis. Virtually allforms of life on Earth depend on this green plant production of organicmolecules to produce the chemical energy that facilitates growth andreproduction. Therefore, the ¹⁴C that forms in the atmosphere eventuallybecomes part of all life forms and their biological products, enrichingbiomass and organisms which feed on biomass with ¹⁴C. In contrast,carbon from fossil fuels does not have the signature ¹⁴C/¹²C ratio ofrenewable organic molecules derived from atmospheric carbon dioxide.Furthermore, renewable organic molecules that biodegrade to carbondioxide do not contribute to an increase in atmospheric greenhouse gasesas there is no net increase of carbon emitted to the atmosphere.Assessment of the renewably based carbon content of a material can beperformed through standard test methods, e.g., using radiocarbon andisotope ratio mass spectrometry analysis. ASTM International (formallyknown as the American Society for Testing and Materials) has establisheda standard method for assessing the bio-based content of materials. TheASTM method is designated ASTM-D6866. The application of ASTM-D6866 toderive “bio-based materials” is built on the same concepts asradiocarbon dating, but without use of the age equations. The analysisis performed by deriving a ratio of the amount of radiocarbon (¹⁴C) inan unknown sample compared to that of a modern reference standard. Thisratio is reported as a percentage with the units “pMC” (percent moderncarbon). If the material being analyzed is a mixture of present dayradiocarbon and fossil carbon (containing very low levels ofradiocarbon), then the pMC value obtained correlates directly to theamount of biomass material present in the sample. In an aspect,renewable carbon substantially comprises the renewable olefin feedstock10. The percentage of renewable carbon in the renewable olefin feedstock10 may be greater than 80% or greater than 90% or greater than 95% orgreater than 99% on a weight basis.

Returning to the FIGURE, the renewable olefin feedstock 10 includes atleast C₄ olefins, preferably comprising C₃ to C₈ olefins. In an aspect,the renewable olefin stream may comprise one or more carbon numberolefins such as C₃ to C₄ olefins or C₃ to C₅ olefins or C₄ to C₅ olefinsor C₃ to C₆ olefins. The renewable olefins may be derived from theircorresponding alcohols (i.e., C₄ alcohols, especially includingisobutanol), which are typically formed by fermentation or bycondensation reactions of synthesis gas. For example, a feedstock forthe fermentation process can be any suitable fermentable feedstock knownin the art, such as sugars derived from agricultural crops includingsugarcane, corn, etc. Alternatively, the fermentable feedstock can beprepared by the hydrolysis of biomass, for example lignocellulosicbiomass (e.g. wood, corn stover, switchgrass, herbiage plants, oceanbiomass, etc.). In another example, renewable alcohols, such asisobutanols, can be prepared photosynthetically, for example usingcyanobacteria or algae engineered to produce isobutanol and/or otheralcohols. When produced photosynthetically, the feedstock for producingthe resulting renewable alcohols is light, water, and carbon dioxide,which is provided to the photosynthetic organism (e.g., cyanobacteria oralgae). Additionally, other known methods, whether biorenewable orotherwise, for producing isobutanol are suitable for supplying the C₄olefins; the methods described herein are not intended to be limited bythe use of any particular renewable feed source. Typically, therenewable olefin feedstock 10 may comprise greater than 50 wt % olefinssuch as greater than 70 wt % or greater than 80 wt % or greater than 90wt % olefins or greater than 95 wt % or greater than 99 wt % olefins.

Olefin isomer types of the renewable olefin feedstock 10, and of theoligomers produced by oligomerization, can be denominated according tothe degree of substitution of the double bond, as follows:

TABLE 1 Olefin Type Structure Description I R—HC═CH₂ Monosubstituted IIR—HC═CH—R Disubstituted III RRC═CH₂ Disubstituted IV RRC═CHRTrisubstituted V RRC═CRR Tetrasubstitutedwherein R represents an alkyl group, each R being the same or different.Type I compounds are sometimes described as α- or vinyl olefins and TypeIII as vinylidene olefins. Type IV is sometimes subdivided to provide aType IVA, in which access to the double bond is less hindered, and TypeIVB where it is more hindered. In an aspect, the renewable olefinfeedstock 10 may comprise high quantities of Type III olefins such asgreater than 50 wt % or greater than 70 wt % or greater than 85 wt % orgreater than 90 wt % or greater than 95 wt % Type III olefins as afraction of the total olefins in the renewable olefins stream.

As shown in the FIGURE, the renewable olefins (possibly derived andconverted from the C₄ alcohols, for example by dehydration of thealcohol see, e.g., U.S. Pat. No. 4,423,251) are mixed with a diluentstream 14 (discussed in more detail below) prior to entering anoligomerization reactor 16 in the oligomerization zone 12. Althoughdepicted with a single oligomerization reactor 16, the oligomerizationzone 12 may contain any number of reactors.

In the oligomerization reactor 16, at least a portion of the renewableolefins are converted into a mixture of heavier boiling hydrocarbonsincluding jet range hydrocarbons via oligomerization by reacting theolefins using a zeolitic oligomerization catalyst under appropriateconditions. For example, the oligomerization zone 12 may, for example,without limitation, be operated at a temperature from about 100 to about300° C. (212 to 572° F.) and a pressure of from about 689 to about 6895kPa (100 to 1000 psig). For example, the operating temperature may befrom about 120 to about 280° C. (248 to 536° F.), or even from about 160to about 260° C. (320 to 402.8° F.). The operating pressure may, forexample, be from about 1034 to about 5516 kPa (150 to 800 psi), or evenfrom about 2068 to about 4964 kPa (300 to 720 psi).

The oligomerization catalyst in the oligomerization zone 12 is notlimited to any particular catalyst and may comprise any catalystsuitable for catalyzing conversion of the one or more biorenewable C₃ toC₈ olefins in the olefin stream to olefinic oligomers comprising heavierboiling C₅₊ hydrocarbons, including jet-range hydrocarbons. Theoligomerization catalyst may be any such catalyst known now or in thefuture.

Conventional oligomerization catalysts will generally convert an olefinto a mixture of dimers, trimers, tetramers, and sometimes pentamers, ofthe olefin. For example, where the C₃ to C₈ olefin is isobutylene, a C₄olefin, the products of oligomerization in the presence of aconventional oligomerization catalyst include C₈, C₁₂, C₁₆, andsometimes C₂₀ olefins, together in a mixture. Conventionaloligomerization catalysts include, without limitation, solid phosphoricacid (“SPA”) and certain ion exchange resins such as Amberlyst-36(commercially available from The Dow Chemical Company of Midland, Mich.,U.S.A.). The olefinic oligomer mixture produced using conventionaloligomerization catalysts may be further subjected to a separationprocess to produce a mixture of jet-range hydrocarbons suitable for useas jet fuels. These jet fuels often have a boiling point distributionthat has well-defined boiling point steps corresponding to only a fewisomers of the corresponding trimer, tetramer, and pentamer paraffins ofthe starting olefin, which is different from petroleum-derived jetfuels.

Alternative oligomerization catalysts comprising zeolite materials, onthe other hand, catalyze oligomerization conversion of C₃ to C₈ olefinsto dimers, trimers, tetramers, and sometimes pentamers of the C₃ to C₈olefins, but also catalyze backcracking conversion of the resultingheavier olefinic oligomers back into lighter and more random and variedsizes of olefins including C₅ to C₂₀₊ hydrocarbons. In other words,under appropriate conditions, zeolitic catalysts such as, withoutlimitation, MTT, TON, MFI, and MTW, yield C₅₊ hydrocarbons, includingjet-range hydrocarbons, with an increased distribution and variety ofcarbon numbers than those made using conventional non-zeoliticcatalysts. This means that jet-range fuel produced from biorenewableolefins via oligomerization in the presence of zeolite catalysts has aboiling range and compositional profile that is more similar tojet-range fuels produced from petroleum refining processes.

Suitable zeolite catalysts may comprise between 5 and 95 wt % of zeolitematerial. Suitable zeolite materials include zeolites having a structurefrom one of the following classes: MFI, MEL, ITH, IMF, TUN, FER, BEA,FAU, BPH, MEI, MSE, MWW, UZM-8, MOR, OFF, MTW, TON, MTT, AFO, ATO, andAEL. 3-letter codes indicating a zeotype are as defined by the StructureCommission of the International Zeolite Association and are maintainedat http://www.iza-structure.org/databases/. UZM-8 is as described inU.S. Pat. No. 6,756,030. In a preferred aspect, the zeolite catalyst maycomprise a zeolite with a framework having a ten-ring pore structure.Examples of suitable zeolites having a ten-ring pore structure includeTON, MTT, MFI, MEL, AFO, AEL, EUO and FER. The oligomerization catalystcomprising a zeolite having a ten-ring pore structure may comprise auni-dimensional pore structure. uni-dimensional pore structure indicateszeolite materials containing non-intersecting pores that aresubstantially parallel to one of the axes of the crystal. The porespreferably extend through the zeolite crystal. Suitable examples ofzeolite materials having a ten-ring uni-dimensional pore structure mayinclude MTT. In a further aspect, the oligomerization catalyst comprisesan MTT zeolite.

The zeolite catalyst may be formed by combining the zeolite materialwith a binder, and then forming the catalyst into pellets. The pelletsmay optionally be treated with a phosphorus reagent to create a zeolitehaving a phosphorous component between 0.5 and 15 wt % of the treatedcatalyst. The binder is used to confer hardness and strength on thecatalyst. Binders include alumina, aluminum phosphate, silica,silica-alumina, zirconia, titania and combinations of these metaloxides, and other refractory oxides, and clays such as montmorillonite,kaolin, palygorskite, smectite and attapulgite. preferred binder is analuminum-based binder, such as alumina, aluminum phosphate,silica-alumina and clays.

One of the components of the zeolite catalyst binder utilized herein isalumina. The alumina source may be any of the various hydrous aluminumoxides or alumina gels such as alpha-alumina monohydrate of the boehmiteor pseudo-boehmite structure, alpha-alumina trihydrate of the gibbsitestructure, beta-alumina trihydrate of the bayerite structure, and thelike. suitable alumina is available from UOP LLC under the trademarkVersal. preferred alumina is available from Sasol North America AluminaProduct Group under the trademark Catapal. This material is an extremelyhigh purity alpha-alumina monohydrate (pseudo-boehmite) which aftercalcination at a high temperature has been shown to yield a high puritygamma-alumina.

A suitable zeolite catalyst may be, for example, prepared by mixingproportionate volumes of zeolite and alumina to achieve the desiredzeolite-to-alumina ratio. In an embodiment, the MTT content may be about5 to 85 wt %, for example about 20 to 82 wt % MTT zeolite, and thebalance alumina powder will provide a suitably supported catalyst.silica support is also contemplated.

Monoprotic acid such as nitric acid or formic acid may be added to themixture in aqueous solution to peptize the alumina in the binder.Additional water may be added to the mixture to provide sufficientwetness to constitute a dough with sufficient consistency to be extrudedor spray dried. Extrusion aids such as cellulose ether powders can alsobe added. preferred extrusion aid is available from The Dow ChemicalCompany under the trademark Methocel.

The paste or dough may be prepared in the form of shaped particulates,with the preferred method being to extrude the dough through a diehaving openings therein of desired size and shape, after which theextruded matter is broken into extrudates of desired length and dried.further step of calcination may be employed to give added strength tothe extrudate. Generally, calcination is conducted in a stream of air ata temperature from about 260 to about 815° C. (500 to 1500° F.). The MTTcatalyst is not selectivated to neutralize acid sites such as with anamine.

The extruded particles may have any suitable cross-sectional shape,i.e., symmetrical or asymmetrical, but most often have a symmetricalcross-sectional shape, preferably a spherical, cylindrical or polylobalshape. The cross-sectional diameter of the particles may be as small as40 μm; however, it is usually about 0.635 mm (0.25 inch) to about 12.7mm (0.5 inch), preferably about 0.79 mm ( 1/32 inch) to about 6.35 mm(0.25 inch), and most preferably about 0.06 mm ( 1/24 inch) to about4.23 mm (⅙ inch).

Returning to the FIGURE, An oligomerized effluent 18 from theoligomerization zone 12 may be passed to a separation zone 20 including,for example, a distillation column 22. In the separation zone 20, theoligomerized effluent 18 may be separated into a light hydrocarbonstream 24 comprising C⁴⁻ hydrocarbons, a naphtha hydrocarbon stream 26comprising C₅ to C₇ hydrocarbons, and a heavy stream 28 comprising C₈₊olefins. As will be appreciated, there may be some overlap between thecomponents of the various streams. For example, the naphtha hydrocarbonstream 26 may include some C₄ hydrocarbons or some heavier hydrocarbonssuch as C₈ or C₉ hydrocarbons. It is preferred that such streams includeat least 50% of the intended components (i.e., the naphtha hydrocarbonstream 26 comprises 80% C₅ to C₇ hydrocarbons).

The further processing of the light hydrocarbon stream 24 and thenaphtha hydrocarbon stream 26 are not necessary for an understanding orpracticing of the present invention. However, the naphtha hydrocarbonstream 26 may be recycled to the oligomerization reactor 16 to furtherreact these hydrocarbons into the jet range. As shown in the FIGURE, inthe various embodiments of the present invention, the heavy stream 28 issplit into a first portion 28 a and a second portion 28 b. The firstportion 28 a of the heavy stream 28 is used to dilute the renewableolefin feedstock 10 as the diluent stream 14. The further processing ofthe second portion 28 b of the heavy stream 28 is described below.

The heavy olefins in the first portion 28 a of the heavy stream 28 arerelatively inert in the oligomerization reaction and have a low tendencyto further react with smaller olefins. Thus, utilizing the first portion28 a of the heavy stream 28 to control the temperature in theoligomerization reactor 16 is desirable because the heavy olefins areless likely than similar saturated diluents to transfer hydrogen to thesmaller olefins resulting in yield loss. Accordingly, it is contemplatedthat the relative amounts of the first portion 28 a and second portion28 b of the heavy stream 28 are adjusted based upon the amount C₈₊olefins as well as the temperature and temperature rise in theoligomerization reactor 16. If the temperature or temperature rise istoo high, the amount of the first portion 28 a of the heavy stream 28may be increased. The C₈₊ olefins that are used as a diluent will beseparated out in the separation zone 20 and can be utilized again as adiluent to the oligomerization zone 12 or the C₈₊ olefins material canbe processed further in the second portion 28 b of the heavy stream 28.Across a single bed of oligomerization catalyst, the exothermic reactionwill cause the temperature to rise. Consequently, the oligomerizationreactor 16 should be operated to allow the temperature at the outlet tobe over about 25° C. greater but no more than 60° C. greater than thetemperature at the inlet. In some embodiments, this temperaturedifference between the outlet and the inlet of the oligomerizationreactor 16, the ΔT, is at least 25° C. but no more than 40° C. In stillother embodiments, the ΔT is at least 25° C. but no more than 35° C.

As shown in the FIGURE, the second portion 28 b of the heavy stream 28,along with a hydrogen containing gas 30 may be passed to a hydrogenationzone 32 having a hydrogenation reactor 34. Hydrogenation is typicallyperformed using a conventional hydrogenation or hydrotreating catalyst,which may include metallic catalysts containing, e.g., palladium,rhodium, nickel, ruthenium, platinum, rhenium, cobalt, molybdenum, orcombinations thereof, and the supported versions thereof. Catalystsupports can be any solid, inert substance including, but not limitedto, oxides such as silica, alumina, titania, calcium carbonate, bariumsulfate, and carbons. The catalyst support can be in the form of powder,granules, pellets, or the like. Hydrogenation suitably occurs at atemperature of about 150° C. (300° F.) and at a pressure of about 6895kPa (1000 psig). Other process conditions known by those of ordinaryskill in the art may be utilized.

A hydrogenated effluent 36 from the hydrogenation zone 32 willsubstantially comprise saturated hydrocarbons (i.e., paraffins). The astream of hydrogenated effluent 36 may be passed to a separation zone 38having one or more vessels or columns 40 a, 40 b configured to separatethe saturated hydrocarbons into one or more product streams 42 a, 42 b.Additionally, at least a portion of the saturated hydrocarbons may beused as a recycle stream to the hydrogenation zone.

For example, a first column 40 a may separate the hydrogenated effluent36 into a vent gas stream 44 and a saturated distillate stream 46.portion 46 a of the saturated distillate stream 46 may be used as arecycle stream to the hydrogenation zone 32. second column 40 b mayseparate the saturated distillate stream 46 into a saturated jet rangestream 42 a and a saturated diesel range stream 42 b.

Thus, using the processes of the present invention, jet-rangehydrocarbons can be produced from a renewable olefin feedstock withminimal yield loss due to hydrogen transfer to the lighter olefins fromheavy hydrocarbons in a diluent stream.

It should be appreciated and understood by those of ordinary skill inthe art that various other components such as valves, pumps, filters,coolers, etc. were not shown in the drawings as it is believed that thespecifics of same are well within the knowledge of those of ordinaryskill in the art and a description of same is not necessary forpracticing or understating the embodiments of the present invention.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention, it being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims and their legal equivalents.

1. process for producing hydrocarbons comprising: oligomerizing arenewable olefin feedstock comprising C₃ to C₈ olefins in anoligomerization reactor containing a catalyst comprising a MTT zeolitethat has not been selectivated and operating the oligomerization reactorunder conditions to produce an oligomerized effluent; separating theoligomerized effluent to produce a light hydrocarbon stream, a naphthahydrocarbon stream and a heavy stream comprising C₈+ olefins; splittingthe heavy stream into a first portion and a second portion; and,diluting the renewable olefin feedstock with the first portion of theheavy stream.
 2. The process of claim 1 further comprising: controllinga flow rate of the first portion of the heavy stream.
 3. The process ofclaim 2 wherein the flow rate of the first portion of the heavy streamis controlled to obtain a ΔT from an inlet to an outlet in theoligomerization reactor of at least 25° C. and no more than 60° C. 4.The process of claim 1 further comprising: hydrogenating the secondportion of the heavy stream in a hydrogenation zone having ahydrogenation reactor to provide a hydrogenated stream.
 5. The processof claim 4 further comprising: separating the hydrogenated stream into avent gas stream and a saturated distillate stream.
 6. The process ofclaim 5 further comprising: separating the saturated distillate streaminto a saturated jet range stream and a saturated diesel rangehydrocarbons stream.
 7. The process of claim 5 further comprising:recycling at least a portion of the saturated distillate stream to thehydrogenation zone.
 8. process for producing hydrocarbons comprising:passing a renewable olefin feedstock comprising C₃ to C₈ olefins to anoligomerization reaction zone comprising an oligomerization reactorcontaining a catalyst comprising a non-selectivated MTT zeolite andwherein said oligomerization reactor is operating under conditions toproduce an oligomerized effluent; passing the oligomerized effluent to afirst separation zone to provide at least one stream comprising C⁷⁻hydrocarbons and a C₈₊ olefin stream; splitting the C₈₊ olefin streaminto a first portion and a second portion; and, recycling the firstportion of the C₈₊ olefin stream to the oligomerization reaction zone.9. The process of claim 8 further comprising: combining the firstportion of the C₈₊ olefin stream with the renewable olefin feedstock toprovide a combined stream; and, passing the combined stream into theoligomerization reactor.
 10. The process of claim 8 wherein the firstseparation zone produces a light hydrocarbon stream and a naphthahydrocarbon stream.
 11. The process of claim 8 further comprising:passing the second portion of the C₈₊ olefin stream to a hydrogenationzone having a hydrogenation reactor containing a catalyst and beingoperated to provide a hydrogenated effluent.
 12. The process of claim 11further comprising: passing the hydrogenated effluent to secondseparation zone to provide at least a vent gas stream and a saturatedjet range stream.
 13. The process of claim 12 further comprising:recycling a portion of the hydrogenated effluent to the hydrogenationzone as a recycle stream.
 14. The process of claim 13 furthercomprising: combining the recycle stream and the second portion of theC₈₊ olefin stream into a combined stream; and, passing the combinedstream to the hydrogenation reactor.
 15. The process of claim 11 furthercomprising: passing the hydrogenated effluent to a second separationzone having at least two columns.
 16. The process of claim 15 wherein afirst column in the second separation zone separates the hydrogenatedeffluent into a vent gas stream and a saturated distillate stream. 17.The process of claim 16 wherein a second column in the second separationzone separates the saturated distillate stream into a saturated jetrange stream and a saturated diesel stream.
 18. The process of claim 17further comprising: passing at least a portion of the saturateddistillate stream to the hydrogenation reaction zone as a recyclestream.
 19. The process of claim 8 further comprising: controlling atemperature rise in the oligomerization reactor by adjusting a flow rateof the first portion of the C₈₊ olefin stream.
 20. The process of claim8 further comprising: increasing a flow rate of the first portion of theC₈₊ olefin stream to decrease a temperature rise in the oligomerizationreactor.